1. Field of the Invention
This invention pertains to catalysts comprising two cations coordinated within a single ligand molecule. Such catalysts catalyze the oxidation of phenols selectively at the ortho position with molecular oxygen under mild conditions.
2. Description of the Prior Art
Organic structures chelating two metal cations have received considerable attention in the past because of their ability, particularly those containing cobalt, to bind oxygen reversibly in the form of a dioxygen bridge between the cations. Martell in Accts. Chem. Res. 15 155 (1982) reviewed the art and reported the oxygenation and equilibrium quotients of some binuclear cobalt complexes comprising two diethylenetriamine chelating centers doubly bridged to form macrocycles.
In various forms, copper catalysts, to which the instant invention particularly pertains, have long been known to catalyze numerous reactions. Reilly in U.S. Pat. No. 3,987,068 reviewed the art of copper complex catalyzed oxidation of phenols and their derivatives, and taught the catalyzed oxidation with dioxygen of substituted and unsubstituted phenols and 1-naphthols at the 4-position. Reilly taught catalysts comprising Cu(I) and Cu(II) salts in complexing nitrile solution such as acetonitrile under substantial oxygen pressure at temperatures to 100.degree. C.
At least two natural proteins appear to contain proximate copper atoms which seem to participate in unique reactions with dioxygen. One such protein, hemocyanin, reversibly binds dioxygen while another, tyrosinase, activates dioxygen whereby to catalyze the oxidation of organic substrates under mild conditions. The subject has been reviewed by Solomon in Copper Proteins (T. G. Spiro, editor) John Wiley & Sons, New York, N.Y. 2 Chpt. 3 (1981).
It is an object of this invention to provide proximate metal cation complexes which catalyze the oxidation of substrates under mild conditions in a manner analogous to that of the above-mentioned metalloproteins. A number of art complexes containing two metal cations in a single synthetic organic ligand are reported in the art: the so-called "ear muffs" of Bulkowski et al, J. Chem. Soc. Chem. Commun. 498 (1977); binucleating macrocycles of Couglin et al J. Am. Chem. Soc. 102 7616 (1980), Couglin et al J. Am. Chem. Soc. 101 265 (1979), Agnus et al, J. Am. Chem. Soc. 101 3381 (1979); Schiff bases reviewed by Groh, Isr. J. Chem. 15 277 L (1976/77) and taught by Grzybowski et al, Inorg. Chem. 19 2604 (1980), Gagne et al, J. Am. Chem. Soc. 101 6917 (1979), Fenton et al, J. Am. Chem. Soc. 100 1931 (1978), and Nelson, Inorg. Chim. Acta 62 39 (1982); so-called "wishbones" of Karlin et al, J. Chem. Soc. Chem. Comm. 881 (1981) Martell, Acc. Chem. Res. 15 155 (1982) as mentioned earlier, McKee et al, J. Am. Chem. Soc. 103 7000 (1981); cyptands of Lehn, IUPAC, Frontiers of Chemistry, Ed. K. J. Laidler, Pergamon Press 265 (1982); and open face macrocycles of Martin et al, J. Am. Chem. Soc. 104 1434 (1982).
Pasquali et al in Inorg. Chem. 17 1684 (1978) reported a mononuclear Cu(I) carbon monoxide complex of diethylenetriamine. Di Cu(I) macrocyclic complexes are not reported.